1. Field of the Invention
The present invention relates, in general, to electromagnetic actuating devices and, specifically, to linear positioning devices utilizing electromagnetic actuating means to control the incremental advance of a movable member.
2. Description of the Relevant Art
Electromagnetic actuating devices have been employed to incrementally advance a magnetic member upon repeated energization of the device. Such devices utilize an electrical coil and a magnetic core including at least one movable core member which is attracted to another portion of the core by the magnetic flux induced in the core when electric current is applied to the coil.
Numerous configurations for electromagnetic actuating devices have been devised for different applications and some include a plurality of coils and movable cores for variable, discrete advance of a movable core depending upon the magnitude of the current applied to the coils or the numbers of coils which are energized. Other incremental positioning devices simply operate in an on/off mode, that is, the movable member moves to one position when the coil is energized and then returns to the start position when current is removed from the electric coil.
Spring biasing means have also been employed to reset the movable core to its start position spaced from the other core portion when the electric current is removed from the coil. Pawl and latch devices have been employed in such linear actuators to hold the movable member in a stationary advanced position after current has been removed from the coil.
U.S. Pat. No. 4,835,425, issued to the same inventor as the subject invention, discloses a novel linear motor which incrementally advances a movable member or workpiece in a stepwise fashion upon each repeated, successive energization of the motor. The linear motor disclosed in U.S. Pat. No. 4,835,425 utilizes latches in the form of a pair of cams associated with the plunger and the pole member of the motor which latch the plunger and the pole member in each incremental advanced position after each successive energization of the electric coil.
While the linear motor disclosed in U.S. Pat. No. 4,835,425 provides a unique approach to incremental advance of a movable member, it has been found that certain improvements could be made to this linear motor in the areas of size, manufacturing cost and to simplify its construction and operation. It would also be desirable to provide such a linear motor with means for selectively releasing the latch means so as to enable the pole member and the plunger and the connected movable member or workpiece to be retracted to a home or start position.